Package carriers are commonly used by electronic circuit manufacturers for holding individual packages during labeling, testing, organizing, sorting, and/or packaging for shipment of the ICs. The carriers also frequently are designed to provide a surface which is adapted for engagement with pick and place tools used to handle and transport the packages during testing, labeling, etc. procedures. The carriers also are designed to protect the packages, and particularly the fragile electrical leads which extend from the encapsulated IC. A packaged IC typically is inserted into a carrier by inserting the pins which extend from the encapsulated portion into holding elements in the carrier.
There are many types of standardized and non-standardized package configurations such as dual in-line pin (DIP) packages, single in-line (SIP) packages and TO-type packages. In TO-type packages, the package is cylindrical with parallel leads arranged in a circular pattern extending from the bottom surface of the package. Each of the above-noted exemplary package types are available in various standardized and non-standardized sizes with various numbers of leads. In TO packages, The microcircuit die is packaged within a cylindrical metal enclosure. The enclosure generally comprises two pieces which are secured to each other during packaging. In particular, a cylindrical metal can which is closed on all sides except for the bottom is fitted over and secured to a circular metal plate which forms the bottom surface of the package. The circular plate has a diameter slightly larger than the can such that a flange extends laterally from the bottom surface of the package. Parallel leads extend downwardly from the bottom plate parallel to the axis of the cylindrical can. The leads are arranged in a circle around the periphery of the bottom plate. Also, a button protrudes from the central portion of the bottom surface of the package. FIG. 1 illustrates a TO-package as described above, but including features in accordance with the present invention. Those features will be discussed more fully in the Detailed Description of the Invention section.
The primary purposes of package carriers are (1) to protect the package, (2) to provide a carrier which can be handled by automated equipment for picking and placing, and (3) to retain the package securely in the carrier. With respect to item 3, many ICs must undergo vigorous vibration or shake testing in order to assure that the IC will operate reliably in particular environments. Most ICs which are designed for use in automobiles, aircraft and almost any military application must be able to survive significant vibration or shake testing as well as other testing procedures before they are sold.
It is important that the package not vibrate loose from the carrier when undergoing such vibration or shake testing. In fact, certain types of ICs, particularly those which include a suspended micromechanical structure such as might be included in an acceleration sensor IC, are subject to vibration testing, not only to test the reliability of the IC, but to obtain an output signal during vibration testing. In particular, the carrier is subjected to a known acceleration or vibration and its output is observed to determine if the IC measures the mechanical acceleration accurately. For such ICs, it is particularly important that the IC package be securely fixed to the carrier such that the acceleration or vibration to which the IC is subject is the same as that applied to the carrier. If the package is not securely fixed within the carrier, then the known acceleration or vibration applied to the carrier will not be accurately transferred to the package (and thus the IC). Thus, the IC will be subject, not to the highly calibrated acceleration force desired, but to some unknown force. This will make it impossible to accurately test the precision of the IC's measurement of the acceleration.
U.S. Pat. No. 5,058,742 discloses an electronic circuit carrier of the type to which the present invention pertains. That patent discloses a circuit carrier for a TO-type packaged device comprising a main body section and a tower section which extends above and below the plane of the main body. The tower is of a generally known configuration including eight triangular pyramidal openings spaced equi-angularly about the axis of the tower and positioned about the outer perimeter thereof. Positioned intermediate to the ends of the openings are oversized holes through which the leads of the TO packaged device are inserted. The leads engage and deflect resilient fingers molded integrally within the channels and positioned just below the holes in the tower section. The fingers resiliently press the leads into the channel and maintain them in their desired position. The top of the tower section is designed with a raised central flat surface so that only the button extending downwardly from the center of the package rests on the tower. Since the bottom surface of the package is supported in the carrier only on the centrally located button, the package can be easily rocked back and forth in the carrier by force applied to the can. Since the leads are forceably captured in the carrier, rocking of the can may cause the leads to bend.
U.S. Pat. No. 4,928,934 discloses a similar carrier for an integrated TO packaged IC including a plurality of stiffly flexible arms projecting upwardly from the tower portion of the carrier which, when a package is inserted in a carrier, bear against the flange of the package and have an inward projection with a horizontal portion which lodges against the flange surface to retain the package in the carrier. In this carrier also, only the centrally located button on the bottom surface of the package contacts the upper surface of the tower. Accordingly, even though the package is better retained in the carrier by the clips, the package still can be rocked easily by a force applied to the can.